I. Field of the Invention
The present invention relates to apparatus and method for using a reactor in a circuit containing a semiconductor device.
II. Description of the Prior Art
In general, when the polarity of a voltage applied to a semiconductor device such as a diode is abruptly inverted, the diode temporarily loses its initial function, so that a reverse current flows therethrough. Although the diode recovers its initial function after a short period of time (recovery time), the diode may break down if the reverse current (i.e., a spike current) is large. Furthermore, when resonant elements such as a coil and a capacitor are used in a circuit in which a current spike occurs, the current spike results in ringing for a considerably long period of time. The current spike and ringing disables normal operation of the circuit. Furthermore, these spurious components become noise components mixed in an output from the circuit. In addition to this disadvantage, an electromagnetic noise component is generated due to an abrupt current flow reversal. In other words, noise components are radiated in space in the form of radio waves. The current spike, ringing, and electromagnetic noise are decisive spurious components in preventing large current control in a high frequency region. This typically occurs in a semiconductor circuit such as a switching power supply circuit.
In order to eliminate the current spike, ringing and electromagnetic noise, a reactor is connected in series with a semiconductor device in the circuit. The reactor includes a core having a through hole in the vicinity of the center thereof and a conductor wound around the core through the through hole. The core is insulated from the conductor. A conventional reactor includes a ferrite or permalloy core. However, when a ferrite core is used, since a squareness ratio (Br/B.sub.1) and a saturated magnetic flux density are small, the operation of the core is degraded. In order to obtain efficient operation of the core, the core size must be increased. When a permalloy core is used, it has a high coercive force (Hc) which degrades the high frequency characteristics, resulting in inconvenience.